1. Field of the Invention
The present invention relates to a holographic device that records/reproduces information by irradiating light beams emitted from a light beam generator onto a recording medium formed with holograms, and more specifically, to a holographic device that records/reproduces holograms that are multi-recorded by an angular multiplexing method by using a light beam having a wide wavelength bandwidth as a reference beam.
2. Description of the Related Art
Conventionally, there have been known storage devices which record information using a holographic principle. A hologram is formed in the recording medium by interference between an encoded object beam and a reference beam. When the hologram is reproduced, a reference beam, having the same wavelength and angle as when the hologram is written, is irradiated onto the hologram to thereby reproduce original information.
The characteristic of the holographic recording medium is that it enables a high density and a large amount of capacity. Further, the information can be multi-recorded by using an angular multiplexing method in which the angle of the reference beam changes, or a wavelength multiplexing method in which the wavelength of the reference beam changes, which enables a much higher density. Furthermore, as compared to conventional electronic storage devices which read out information in a sequential manner, the holographic storage devices can read out the information in a page unit at one time. Thereby, high-speed data processing can be realized.
In the angular multiplexing method, a conventional galvano mirror has been used in a holographic device to change the angle of the reference beam. A device, in which holograms multi-recorded by the angular multiplexing method are reproduced by means of the galvano mirror, is disclosed in Japanese Unexamined Patent Application Publication No. 2000-155950, for example.
However, in the conventional holographic devices, a complex driving unit for driving the galvano mirror and a control system for controlling the driving unit have been essential in order to precisely control the irradiation angle of the reference beam with respect to the recording medium. For this reason, it has been difficult to miniaturize the holographic device, to reduce a manufacturing cost thereof, and to ensure high reliability thereof.
Further, laser light has been used as the reference beam, however, the laser light generally has a very narrow wavelength range. Accordingly, when the irradiation angle of the reference beam with respect to the recording medium deviates slightly, a condition in which a light beam is diffracted by a hologram can not be satisfied, and as a result, the hologram can not be reproduced. Therefore, even in consideration of the above, the angle of the reference beam should be very precisely controlled, which causes the holographic device to be expensive.